This invention relates to material handling apparatus and more particularly to a pallet molded of synthetic resin material or the like adapted to form part of a container for transporting, supporting, and storing a load of fine granular, particulate, powdered or other fluidizable material, and for fluidized unloading of the load from the container.
The pallet of this invention represents an improvement over the container disclosed in the coassigned U.S. Pat. No. 4,007,694, and commercially available from the assignee of this invention, Semi-Bulk Systems, Inc. of St. Louis, Mo. under their registered trademark AIR PALLET. The pallet disclosed in the above-noted patent is generally circular, as viewed from above, having a number of legs spaced for the entrance of the tines of a forklift from any of four directions. The pallet has a peripheral wall extending around the pallet and an upwardly facing deck supported by the peripheral wall for supporting the load. The deck slopes downwardly toward one side of the pallet and is adapted to have a porous diaphragm of cloth or the like secured thereto with the diaphragm covering the deck. An outlet opening is provided in the peripheral wall of this prior art pallet above the level of the deck at the lowest side thereof through which the powdered load may be discharged or unloaded. An inlet opening also extends through the peripheral wall for introducing compressed air into the space between the diaphragm and the deck. The compressed air flows upwardly through the porous diaphragm for fluidizing the powdered load bearing against the diaphragm.
The diaphragm of this prior art container was secured to the pallet by a spline held in place within a groove by means of staples driven into the pallet. The spline merely distributed the loading of the diaphragm to the staples. However, upon fluidizing the load in this prior pallet, the air pressure beneath the diaphragm would, on occasion, apply tension loading on the staples and pull them free of the pallet thereby releasing the diaphragm and preventing fluidization of the remaining portion of the load. When the diaphragm pulled loose, refurbishment of the pallet was required prior to reuse.
In many uses of the container of this invention, such as where the empty containers must be air transported or where the containers are used to contain toxic materials, it is desirable that essentially all of the material be emptied from the container during unloading thereby to minimize spilling of the material during handling of the empty containers.
The prior art container described in the above-mentioned patent had a tubular plastic film bag secured to its pallet. This bag was generally of the same diameter as the pallet (e.g., about 42 inches in diameter) and was of sufficient height to contain a desired quantity of powder (e.g., 500-4,000 pounds or more). The bag was typically attached to the peripheral wall of the pallet by means of a metal strap band on the outside of the bottom of the bag, tightened therearound and secured in place. Typically, this strapping band was of the well known type (nylon) used to band shipping containers commercially available from Signode Corporation of Chicago, Ill. and other companies. Upon pressurizing the interior of the bag during fluidized unloading of the load, the air pressure would, on occasion, pull the bag from between the strap and the pallet with the resultant loss of fluidization air and spillage of the powdered load. Although this rarely occurred, it was a serious problem when it did occur because the escaping powder often prevented resealing of the bag to the pallet and thus the load could not be fluidized for unloading and would continue spilling from the container. It was also recognized that because the pallet was preferably molded of synthetic resin material, it suffered from some degree of inherent dimensional instability and it would relax when a strap was tightly applied therearound.
It was also found that the pressure buildup within the container would reduce fluidizing air volume to merely equal the volume of powder and air discharge from the container thus limiting the degree of fluidization and the discharge of material from the container.
Due to the flow of material into the container during filling and due to the flow of air through the fluidized material and the flow of the fluidized material from the container during unloading, it has been found that a static electricity charge could build up on the container and pose a danger when handling potentially explosive or flammable materials or when unloading relatively safe materials in a hazardous environment (e.g., in a hydro carbon environment).
Still further, the discharge conduit on prior art containers would, on occasion, pull loose from the pallet during unloading or would not properly seal relative to the pallet with consequent leakage of the material during unloading.